
\begin{tikzpicture}[scale=2.4]
  \coordinate (P1) at (0:1);
  \coordinate (P2) at (72:1);
  \coordinate (P3) at (144:1);
  \coordinate (P4) at (-144:1);
  \coordinate (P5) at (-72:1);
  \draw (0,0) circle (1);
  \foreach \fromdot in {P1,P2,P3,P4,P5} {
    \foreach \todot in {P1,P2,P3,P4,P5} {
      \draw (\fromdot) -- (\todot);
    }
  }
\end{tikzpicture}
